Arcane/Fire mages have frost nova too.  And Frostbolt (rank 1) for kiting.  And ice lance for easy 1-2K damage after frost nova.  And cone of cold.  And blizzard (rank 1) for finding stealthers in bg's.  And NOW, Ice block.  And, well, you get the point. 

All this, plus improved counterspell, extra intellect, Spell Power, clearcasting, Arcane Power (extra crit dmg), improved scorch, ignite, 70% chance to resist pushback on fire spells, mana regen while casting (lol, almost never run out of mana if only use scorch), Blastwave, and of course, Presence of Mind and Pyroblast (although that's really pretty insignificant in the overall picture). 

Not to mention an additional 10% chance to crit with scorch (4+6), 3% more crit chance from Arcane Instability, and an additional 3% chance to crit with all spells due to clearcasting (10% * 30%).

If you know how to use ALL of your spells, you will own in PvP, no matter what spec, but as you can probably guess, I have a great time with arcane/fire (33/28, scorch spec), but only when I use the frost spells properly.